1. Field
Exemplary embodiments of the present invention relate to an analog-to-digital converter and, more particularly, to an analog-to-digital converter that corrects an error generated therein.
2. Description of the Related Art
An analog-to-digital converter converts an analog signal to a digital signal. The analog-to-digital converter is used in an apparatus that processes digital signals. For example, an image sensor receives optical signals (i.e, analog signals) from an external source, converts the optical signals into digital signals, and processes the digital signals. The image sensor includes a pixel array, for receiving the optical signals, and an analog-to-digital converter provided in each column of the pixel array to read a large amount of data at high speed. The analog-to-digital converter used in the image sensor needs to operate with low power, occupy a small area and have high resolution.
In this regard, a successive approximation register (SAR) analog-to-digital converter is used. The SAR analog-to-digital converter has advantages of fast conversion speed and low power consumption because it may convert one bit into a digital signal during one clock cycle. However, since a capacitor array that occupies a large area is included in the SAR analog-to-digital converter, it may not be applied to devices with limited available fabrication area, such as an image sensor.
Furthermore, when a comparator in the SAR analog-to-digital converter performs a comparison operation, an abnormal value may be outputted due to noise occurring in the circuit. Particularly, in the image sensor, since many SAR analog-to-digital converters are driven, the comparator may not normally perform the comparison operation due to limitations in drivability of a reference voltage, so that an error may occur in a digital signal (i.e. an output signal of an analog-to-digital converter).
Korean Application Patent Publication No. 2010-0031831 discloses an SAR analog-to-digital converter with multiple stages for correcting errors.